1. Field
The present disclosure relates to a positive active material for a lithium secondary battery.
2. Description of the Related Art
Recently, lithium batteries have drawn significant attention as power sources for small portable electronic devices. Lithium secondary batteries using an organic electrolyte have a discharge voltage about twice as high as those batteries using an aqueous alkali electrolyte.
Lithium batteries have been widely adopted along with rapid increase of the demand for portable devices such as wireless telephones, personal digital assistants (PDA), or notebook computers. Recently, lithium batteries have also been used in electrical vehicles. In addition, the demand for high-energy density lithium batteries is significantly increasing as the lithium batteries are increasingly miniaturized and becoming to have higher performance. While the technologies of lithium batteries have been remarkably developed, still better performance is desired.
The energy of a lithium secondary battery is mainly dependant on the positive active material. Commercially available small-sized lithium secondary batteries typically use the layered compound of LiCoO2 as a positive active material. LiCoO2 is an excellent material having stable charge/discharge characteristics, excellent electronic conductivity, high thermal stability, and flat discharging voltage characteristics. However, cobalt (Co) is expensive and so is LiCoO2. The actual electrical capacity of LiCoO2 is in the range of about 140 to about 150 mA h/g, which is 50% of a theoretical capacity thereof.
Currently, LiNiO2, LiCoxNi1-xO2(0<x<2, and M is Ni, or the like), Li2MoO3, and LiMxMn2-xO4 have been actively developed as positive active materials. However, LiNiO2 is difficult to be commercialized due to difficulty in synthesis and its poor thermal characteristics. LiCoxNi1-xO2 does not have good performance to replace LiCoO2 as a positive active material. It has been known that, when layered Li2MoO3, or LiMxMn2-xO4 having a spinel structure, is used as a positive active material, a lithium salt or organic solvent of an electrolyte is dissolved at a high voltage (4.9 V) and a high temperature, and manganese (Mn) or molybdenum (Mo) is eluted by HF generated when the lithium salt reacts with moisture, thereby causing deterioration of charge/discharge characteristics at high temperature environments.